Can someone explain gearing numbers?

Robd263 Posts: 52
edited December 2013 in Road buying advice
Sorry for what I am sure is a basic question but can someone give me a layman explanation of the numbers seen on cassettes e.g. 10-28, 12-32 etc.

I assume certain numbers men lower gears, and easier to climb etc.

What should I be looking for in a bike I want mainly for weekend riding distance and sportive? No plans to race.




  • desweller
    desweller Posts: 5,175
    The numbers refer to the maximum and minimum number of teeth. So, if you have a 10-speed cassette (10 sprockets) and it is a 12-23 then the smallest sprocket has 12 teeth and the largest has 23 teeth.
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  • andrew_s
    andrew_s Posts: 2,511
    edited December 2013
    On the rear, more sprocket teeth means easier climbing. You would see gears like 11-23, 12-28 or 11-34 quoted, which is the range of sprocket sizes on the cassette.
    On the front fewer chainring teeth mean easier climbing. Typical choices would be 53/39, 50/34, 50/40/30 or 44/32/22, according to road or MTB and double or triple.

    If you are using a 44t chainring and an 11t rear sprocket, the wheel goes round four times for each turn of the pedals.
    For 50t and 25t, it's twice, for 30t and 30t, it's once, and for 22t and 32t it's just over 2/3 of a wheel revolution for each turn of the pedals.
    With low gears (eg 1:1) climbing is easier as you don't have to lift youself so far up the hill with each turn of the pedals.
    With high gears (eg 53t &11t = 4.8:1) because you go further with each turn of the pedals, you can go faster before you can't pedal fast enough any more.

    How far you go with a turn of the pedals is also affected by the wheel size - with a bigger wheel you go further.

    Gears are often quoted as (eg) 53 x 14 for the chainring and sprocket sizes. This is normal when it's obvious what the wheel size would be, eg in a discussion about road bikes.
    They are also often quoted as gear inches (in English). These take the wheel size into account, and are calculated as chainring size / sprocket size multiplied by wheel diameter in inches. E.g. 53/14 x 27" = 102" or 22/32 x 26" = 18".
    Continental folk will do a similar thing using the wheel circumference in metres, and call the result "development". E.g. 53/14 x 2.11m = 7.99m. Wheel circumference is often readily available as the cycle computer calibration number.

    For non-competitive sportive riding, I'd recommend a gear range of 30-100 inches, though many macho types will say you don't need to go as low as 30, and if you find it hard you should man up and go out and train more.
    That would be something like 50/34 (compact double) and 11-32 cassette (with MTB rear mech) for double, or 48/38/28 to 12-27 for triple.
    Triple are more fiddly to set up the changing for, and will never be quite as slick, but you can change to lower gears easily, whilst with compact double you are already pretty much as low as you can go.
    Lower gears are likely to be desired if you start carrying touring luggage, if you get faced with something properly steep when you are already tired (eg Kirkstone pass 200 miles into the event), or if you go off to the Alps.
  • me-109
    me-109 Posts: 1,915
    ^^that pretty much says it all. Good post.
  • maddog 2
    maddog 2 Posts: 8,114
    +1 good post Andrew

    if you run a 34/50 compact then a 11-28 or even 12-30 cassette gives a good range for general recreational riding. 12-27 gives smaller gaps but the lowest gear isn't quite as low, so it will depend on how strong you are, how steep the hills are and how you like to ride those hills.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • Thanks for all the advice. That makes things clearer to me now although I will admit I did get lost in the sums converting things to inches.

    So in short are we saying that for sportive riding a 11-28 or above (higher numbers) would be suitable and the higher the second number the easier climbing would be?

    I consider myself a fairly strong rider and I'm relatively fit but hills are the one area I can struggle with when they are long and I would like them to be a bit easier.
  • diamonddog
    diamonddog Posts: 3,426
    Robd263 wrote:
    So in short are we saying that for sportive riding a 11-28 or above (higher numbers) would be suitable and the higher the second number the easier climbing would be?

    Correct :)
  • So the bike I'm currently looking at (which seems to change twice a day too much choice) has 50/34 and 11-28. This seems suitable for what I want the bike for based on my understanding of the above.

    Am I correct?
  • kajjal
    kajjal Posts: 3,380
    Yes that's fine, 12-30 would be even easier if it is very hilly by you but 28 is fine. I have 50/34 and 12-30 but rarely use 30 or the next cog down. Some bikes even have 11-32 which is approaching mountain bike gearing and would get you up anything.